I "inherited" a small project from a person I don't know, and I'm navigating my way through it. It's a small gadget featuring a 7-segment LED display. I hear the device's original designer is more of a hardware guy (the very messy, copy-pasta code hints in the same direction). Thus I'm inclined to think his schematic is something I can learn from, but there are a few things in there which I find puzzling — one of which is this:
Which looks simple enough:
- a single MCU pin cannot drive 7 LEDs directly, so you need a switch transistor;
- you can use either a PNP or PMOS (proper high-side switches), or NPN used as an emitter follower (the anodes only "see" ~4.3V, which is acceptable). He chose the latter, probably because he had a bucketful of NPNs laying around;
- "it's a bipolar transistor, it needs a base resistor"
The 10k resistors seem to be redundant, you can replace them by wires and get a pure emitter follower. Can they serve any reasonable purpose in this situation?